I. Identification/characterization of receptors for GI peptides. I.A. Nature and role of glycosylation of receptors for bombesin-related peptides [mouse gastrin-releasing peptide receptor (mGRP-R) and rat neuromedin B receptor (rNMB-R)]. Using cross-linking, specific glycosidases and functional studies after deglycosylation, the mGRP-R and rNMB-R were shown to be 50 and 35% glycosylated respectively; and to be N-linked complex oligosaccharides. The rNMB-R but not the mGRP-R had terminal sialic acids. All extracellular potential glycosylation sites on both receptors were glycosylated with the mGRP-R having 4 and the rNMB-R having 2. Glycosylation was essential for mGRP-R, but not for rNMB-R G-protein-coupling and high affinity binding. These studies will be coupled with site-directed mutagenesis studies in the future to determine which residues in the GRP-R are important in mediating the high affinity state. I.B. Characterization of GI peptide receptors by development of specific antagonists. 1. GRP-active configuration. Structure-function studies using conformationally restricted amino acid substitutions in GRP were performed in collaboration with Prof. D.H. Coy (Tulane University) and provided evidence to support a putative folded conformation of the receptor bound Bn and the importance of the His/12 in receptor activation. 2. Identification of novel VIP receptor antagonists. The physiological role of the ubiquitous neurotransmitter peptide VIP remains unclear because of the lack of specific receptor antagonist. We applied two strategies used successfully with related peptides. In collaboration with Dr. D.H. Coy, Peptide Research Labs, Tulane University, pseudopeptides of the biologically active NH2 terminus and chimeric peptides were made. Neither approach yield potent antagonists, however VIP (6-28) was found to be 2 times more potent than existing antagonists and should be useful as a starting point to modify to attempt to develop more potent antagonists.